A conventional syringe after being used for medical injection purpose will be treated for waste disposal. If the injection needle mounted on the syringe is protruded outwardly, it may cause infectious contamination or pollution, hazardous to environmental protection and human health. Even some improvements had been made to automatically retract the injection needle into the syringe body to prevent injury or infectious contamination to someone, the retracted needle as spring tensioned may still be inadvertently protruded outwardly by an external force or protruded downwardly when pendently held or when disposed in a garbage yard for an accidentally protruding of the needle to cause injury to the others.